You get a sense early on in this documentary that Mike Tyson has met a formidable opponent. Director James Toback positions his lens straight at the former heavyweight champ, and apart from archival footage of the big fights and the controversial moments out of the ring, the camera doesn't stray. Tyson is the only interviewee, and he can't escape.

On the one hand this makes the film a kind of podium opportunity – a chance for Tyson to confess, to explain and to justify his actions without counter claims. But there is so much space for Toback to get the measure of his subject, and then to point us towards inconsistencies, ambiguities and contradictions, that the film becomes a complex puzzle, not a hagiography.

Toback, who became friends with Tyson after casting the fighter to play himself in two fictional features, clearly respects his subject. There's a palpable sense of mutual trust here, and Tyson speaks frankly about his dark side and his brutal upbringing. We get the story of a man from the Brooklyn slums who learns early in life to impose himself physically on others. The realisation is key to Tyson becoming a street criminal, which lands him in juvenile detention, but it's also the seed of what becomes a problematic attitude towards sex.

Tyson went to jail in the early 90s for rape, and his ex-wife accused him of domestic violence. He denies both these crimes, and in his soft-spoken, measured tones, he is actually convincing. It might surprise people who don't know anything about him that Tyson is very pleasant company: he's thoughtful, self aware and, at times, contrite. But Toback has enough of him on camera to show disturbing glimpses of a man capable of great brutalities. He captures moments where the fighter's language suddenly veers towards the extremely violent, and the anger that still burns inside comes to the surface.

Those who love boxing know what a physically and mentally demanding sport it is – how much discipline is required to succeed in the ring. But only the most naive deny the corruption that lurks in the shadows beyond the ropes. Tyson owes his best and his worst, as a man, to the sport. His fond memories of his early trainer and mentor Cus D'Amato, who taught him to channel his rage, contrast with his accounts of later dealings with the infamous promoter Don King. Both are vivid insights into the moral extremes he's encountered.

In the end this is an unflinching portrait of a man, honest and beguiling. It puts Tyson's sins into context, but never excuses him. In a way, it's also a very American story about success from nothing and the double-edged sword of money and fame. Even if you abhor boxing, if you appreciate well crafted documentary you should see this.